You might think of the Mophie Juice Pack Air as the sports car of the iPhone battery case world: sleek and stylish, and more reliable than the competition. Meanwhile, the Juice Pack Plus is more like a minivan, packing on extra size to bring more capacity to the table. Well, under this analogy, the new Juice Pack Pro is a Sherman Tank. This is a bulky case that adds almost Otterbox-level protection to your iPhone 4 or 4S - but the Juice Pack Pro also provides pretty much the biggest honkin’ battery you could conceivably strap to your iPhone without having to buy Siri a chiropractor.

I’m Gonna Need a Bigger MophieInstalling previous Mophie Juice Packs was simple: Snap your iPhone into the bottom piece, then snap on the top piece. The Juice Pack Pro, however, is a bit trickier. First, you snap your iPhone 4 or 4S into the power sled. Then, you attach the screen cover, and then you install the rubberized outer layer. If you were to imagine combining a traditional Mophie model with a Case-Mate Naked Case, and then combining that with a plain old silicone case, you’d have the right idea. The case also includes a durable belt clip you can attach over your iPhone’s screen when you’re not using the phone, if desired.

If that sounds like a hefty case, it is: The Mophie Juice Pack Pro measures 5.26 X 2.78 X 1.02 inches and weighs about 5.6 ounces (an iPhone 4S weighs about 4.9). If you absolutely need the slimness and lightness provided by your iPhone 4/4S, then this case might not be right for you.

Since previous Mophies didn’t provide any screen protection at all, it’s impressive that the Juice Pack Pro provides a touch-through screen cover. What makes it even more amazing is that Mophie also provides a second, adhesive screen protector in the box! Even with both layers installed, we found the screen to be as responsive and clear as ever. Just make sure that you install the screen protector first and make sure that no debris gets caught between the two layers; otherwise, you may have to take apart the whole case and try again.

Once you have all the layers installed, your iPhone will be completely encased in rugged protection that Mophie says meets or exceeds the MIL-STD 810G military standard. It is resistant to shocks, drops, impacts, and small amounts of moisture (but it is not waterproof).

If you wish, Mophie gives you the option to buy replacements packages for the screen cover and outer rubberized layer in any of 21 different color schemes, which cost about $20 each. This is a unique way of approaching color choice, and it does have the advantage of allowing you to change the color of your case (or replace a damaged component) without having to replace the entire case. However, when you first purchase the Mophie Juice Pack Pro, the only option for the screen cover and rubberized outer layer is black.

If Mophie had allowed you to choose the colors that come with your Juice Pack Pro, or perhaps included a coupon for one free color scheme, we would consider this to be a clever way to make the color scheme of your case adaptable. However, since they didn’t do that, you will find yourself having to spend $20 each buying accessories for your accessory, which makes it feel like Mophie is nickel-and-diming users just because they want to customize their color scheme. Considering this is Mophie’s highest-end, most expensive case, we find this decision to be baffling. (Strangely, the color add-ons include shades like black, white, green, purple, yellow, and silver - but not blue!)

The Juice Pack Pro covers over the Home button, top power button, and volume buttons with its own press-through buttons, which worked well in our testing. The hold switch is accessed by opening a flap on the rubberized outer layer, and similarly another flap covers the sync/charge port (Mophie’s usual mini-USB port; a cable is included). A cutout leaves the camera uncovered. Like many battery cases, four battery charge indicator lights are along the bottom with a button to check the charge level. For some reason, the Juice Pack Pro requires you to press the button to activate the lights even while the device is charging (many battery packs keep the lights on at all times when in charging mode). The power/standby switch for the Juice Pack itself is on the bottom-left side, opposite the charging port. Finally, another flap on top opens to provide access to the headphone jack, but the thick case leaves the jack so recessed that you may want to consider an adaptor or extender of some sort if you don’t use Bluetooth (something like this will do nicely).

Other vendors are already starting to produce accessories that are compatible with Apple’s new Lightning connector, so we’re not sure why Mophie isn’t on board yet. For now, if you have an iPhone 5, Mophie’s Juice Packs won’t do you any good, but Mophie says new Juice Packs are coming soon.

So does this thing actually work? The battery in the Mophie Juice Pack Pro has a capacity of 2500 mAh. (For reference, the Juice Pack Plus is 2000 mAh, the Juice Pack Air is 1500 mAh, and the internal iPhone 4S battery is 1430 mAh.) In order to find out if the Mophie actually lives up to the hype, we suggested it to what might be considered a torture test for smartphone batteries: me. For over eight hours straight, I kept the Mophie on my iPhone 4S as part of my regular schedule. This included lots of audio, video, surfing the web, downloading, games, and a brief phone call. At the end of all that, not only was my iPhone’s internal battery still full, but the Mophie still had two out of four dots full on the charge indicator gauge. Wow.

The Mophie Juice Pack Pro didn’t interfere with any antennas, microphones, or speakers while I was using it. It simply provided an unprecedented amount of charge for my iPhone. This isn’t just enough to get you through the day; it might even be enough to get you through a small natural disaster.

Power! Unlimited Power!If you’re an iPhone owner, you need something from Mophie. If you have an iPhone 5, you’ll have to wait, and if you’re an extremely light user, the Juice Pack Pro might be overkill. Personally, I would rather err on the side of caution. The Juice Pack Pro’s tremendous battery life, combined with its strong physical protection, will give you less to worry about during the day. On the other hand, if you’re more concerned about case price and size, and less concerned about power consumption and physical protection, you might be better off with the Juice Pack Air or Plus, but let’s face it - you still need a Mophie.